1. Field of the Invention
The present invention relates to a slit-lamp biomicroscope for observing (examining) an eye to be examined by illuminating the eye with slit light.
2. Description of Related Art
Observations of an eye to be examined (a patient's eye) using a slit-lamp biomicroscope have been widely used as general examinations in ophthalmology. Normally, a slit-lamp biomicroscope is adjustable in its slit width of illumination light for illuminating the eye to an intended width in accordance with aims of observations.
In addition, some slit-lamp biomicroscopes comprise a plurality of filters inside thereof for changing a color of light or for changing quality of light in order to suppress heat that the illumination light generates. This type of slit-lamp biomicroscope is also capable of selectively inserting an intended filter into an illumination optical path in accordance with aims of observations.
However, in general, as the slit width is made narrower, the illumination light amount decreases, and therefore, the illumination light amount needs to be increased to make up for the light loss. In addition, the illumination light amount decreases when passing through the filters. Because of this light loss, when adjusting the slit width or changing over the filters, an examiner (operator) is required to operate an illumination light adjustment knob or the like in order to adjust the illumination light amount based on his experience. This operation imposes a burden on the examiner and, if it takes long for the adjustment, examination efficiency decreases.
When using the slit light biomicroscope, an examinee's head is supported by a headrest having a chin rest and a forehead rest so that the examinee's head is not allowed to move. Thereafter, the examiner operates a knob or the like to move the chin rest up and down thereby to bring the eye into a predetermined position.
Once the eye is properly positioned, the main body of the biomicroscope is moved as necessary to observe the eye: The microscope comprises two units which are an illumination unit provided with an illumination optical system for emitting the illumination light onto the eye and a microscope unit (observation unit) provided with an eyepiece portion as well as an observation optical system for observing the eye. In the case of observing a cross-sectional image of the eye, the slit width is made narrow. By adjusting an axial angle between an illumination optical axis of the illumination optical system and an observation optical axis of the observation optical system, a cross-sectional image of a cornea, an anterior chamber, a crystalline lens, a vitreous body or other portions of the eye can be observed. However, the knob for moving the chin rest up and down is normally provided near the chin rest, and therefore, the examiner is required to extend his arm to reach the knob every time he operates the knob. Apparently, this is extremely inconvenient.
In addition, in order to observe a cross-sectional image of the eye, the observation optical axis needs to be shifted to right or left to some extent instead of being positioned in the front of the eye. As the result of this shift, the eyepiece portion of the microscope unit is as well shifted to right or left to some extent so that the examiner is forced to observe the eye in uncomfortable posture.